Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed a lightweight, flexible and high-efficiency thermoelectric generator that can harness your body heat to generate a small amount of electricity. The device could be used to extend the battery life of low-power wearable devices.

The big names in personal electronics are constantly pushing for thinner and thinner devices, and while that certainly gives us much sleeker and attractive designs, it also invariably leads to compromises in terms of battery life.

Previous attempts to generate additional power for personal electronics include solar-powered mobile phones and piezoelectric generators that create energy when pressed or bent (the latter was also developed at KAIST). But there is also another way, which may be ideal for low-power wearable devices; and that is to harness the waste heat your body naturally gives off 24/7 through a thermoelectric generator.

The thermoelectric generators developed so far have been based on either organic or inorganic materials. The former are very flexible, but highly inefficient, while the latter have a higher output, but also tend to be heavy and rigid.

Prof. Byung Jin Cho and colleagues at KAIST have managed to harness the best of both worlds by developing a generator that is both flexible and has a comparatively high power output. The researchers did so by first creating liquid-like pastes of n-type and p-type thermoelectric materials, and then embedding them within a flexible and lightweight glass fabric. The materials permeated the glass and formed hundreds of microscopic n-type and p-type dots, orderly arranged next to each other.

The main advantage of this new design is that the device doesn't need additional thick, external layers to mechanically support the structure. In previous designs, this was exactly what made thermoelectric generators bulky, heavy, rigid and inefficient. Instead, in this new design, the glass fabric encloses the thermoelectric materials without sacrificing thickness, flexibility or efficiency, opening up interesting new applications in wearable electronics.

The researchers say that a wristband with an area of 10 x 10 cm (4 x 4 in) using their technology would only weigh about 13 g (0.45 oz) and, at room temperature, output 40 mW of power. Admittedly, that's not a staggeringly high number for most personal electronics (for reference, an iPad 2 requires about 3 W), but it could make a significant difference in low-power wearable devices such as e-paper smartwatches and fitness trackers, but also perhaps smart collars and smart clothing.

Professor Cho also said that the technology may find applications beyond personal electronics, and particularly in automobiles, factories, aircraft, vessels, and systems where a large amount of thermal energy is being wasted.

A paper describing the device has been published in the journal Energy & Environmental Science.

Source: KAIST

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